1. Field of the Invention
The present invention relates to a method of determining the position of objects in equipment comprising at least one transducer designed to receive signals from a set of objects arranged to emit signals that propagate linearly between the objects and the transducer, and members arranged to produce direction-defining signals that define the direction of the sight lines from the transducer to the objects in relation to the transducer.
The invention also relates to an arrangement for creating a set of objects with known positions for equipment of the above type.
2. Description of the Related Art
The following terms are used in this application:
the location of an object is defined by the position and/or orientation of the object; PA1 the position of an object is determined by a number of translation coordinates; PA1 the orientation of an object is determined by a number of rotational coordinates.
Furthermore, the term object denotes an object able to emit signals that can be received by the transducer, that is to say signals that propagate linearly between the object and the transducer. Such signals are primarily optical signals with frequencies within the visible wavelength range or outside this range, such as infrared light. Examples of objects are light sources (e.g. light bulbs or light-emitting diodes), reflectors (e.g. markers of reflecting tape) or details of the transducer's surroundings identifiable by means of image analysis (e.g. corners, holes, light points or markers having a certain shape and with a colour or brightness that deviates from the surroundings). Alternatively other signal forms may be used, e.g. ultrasonic or microwave signals, in which case the objects, for instance, consist of sources or reflectors for these signals, for instance.
A position transducer arrangement is known through the Swedish patent specification No. 444 530. This arrangement preferably utilizes optical signals. An optical transducer is designed to sense the direction from the transducer to each of a number of light sources, whose positions in relation to each other are known. The transducer determines the directions to at least three such light sources. The arrangement has calculation means which, on the basis of the directions thus determined, determine the angles between the sight lines from the transducer to the light sources and which, on the basis of these directions and angles and of the known positions of the light sources in relation to each other, calculate the transducer's position and possibly also its orientation in relation to the light sources.
A position transducer arrangement operating in accordance with a similar principle is known through Swedish patent specification No. 458 427. Its transducer consists of a device that generates a two-dimensional image of its surroundings. An image-analysis system receives the information content of the image and scans the image for a number--at least three--of recognizable, predetermined details in the surroundings having known positions in relation to each other. The image analysis system determines the position of the details in the image. The arrangement also includes calculation means that, from the positions of the details in the image, determine the directions of the sight lines from the transducer to the details, from the directions determine the angles between the sight lines and, on the basis of these directions and angles and of the known relative positions of the details, calculate the position of the transducer and possibly also its orientation in relation to the details.
The older Swedish patent application No. 9403255-4 describes a control equipment utilizing a control device carried by an operator, e.g. in the form of a free handle. The control device has a transducer operating on the same principle as the transducers described in the two preceding paragraphs. With the aid of the transducer the directions are determined to a number of objects (e.g. light sources, markers or details identifiable in the surroundings by image analysis) with known relative positions. The equipment also has means which, on the basis of the directions thus determined, calculate the angles between the sight lines to the object and which, on the basis of these directions and angles and of the known positions of the objects, determine the position of the control device and possibly also its orientation in relation to the objects.
Equipment of the type described above requires that the transducer always has at least three objects with known positions within its field of vision (four objects are required for some configurations). A typical transducer of this type has a certain working range within which it can alter location, i.e. position and/or orientation during use. To ensure that the transducer always has a sufficient number of suitably positioned objects within its field of vision, regardless of its actual location in the working range, therefore, more than three objects are generally required, and if the working range is large a relatively large number of objects is required. The relative positions of these objects must be known with great accuracy. The positions of the objects must therefore be measured both when the equipment is commissioned and if the working range is to be extended or altered.
Known measuring methods employing distance and/or angle measurement, triangulation or the like have hitherto been used to determine the positions of objects in equipment of the type in question. Determination of the positions to the high degree of accuracy required demands special equipment, e.g. theodolites, and expert knowledge, as well as being complicated and time-consuming. These circumstances have generally entailed a considerable practical and economic drawback.